1. Field of the Invention
The present invention relates to an optical deflector and an optical switch, more specifically an optical deflector which can retain a deflected state obtained when a drive voltage was applied even after the drive voltage is turned off, and an optical switch including such the optical deflector.
2. Description of the Related Art
Because light enables high-velocity data transmission, optical communication is dominant in the long-distance transmission, such as the fundamental communication system. Recently the transmission band has been on increase while WDM (Wavelength Division Multiplex) technique has been developed. The optical communication has increasingly higher velocity and larger capacities. In the optical communication system, expansion of a WDM network from 1 versus 1 coupling to coupling between plural points requires an optical deflector for switching optical signals to different transferees.
As a conventional optical deflector is known the element using the mechanical micro mirror. For higher integration, higher velocity and lower losses, optical deflectors utilizing refractive index changes due to the electrooptical effect of ferroelectric materials have been also developed. In constituting the WDM network the latter optical deflector is very prospective. The electrooptical effect is the phenomena that refractive indexes of a substance are changed by application of electric fields.
Optical deflectors utilizing refractive index changes due to the electrooptical effect of ferroelectric materials are proposed by, e.g., Q. Chen et al. and described in the Laid-Open Japanese Patent Application No. Hei 09-5797.
The optical deflectors proposed by Q. Chen et al. are an optical deflectors using a prism domain inversion and an optical deflectors using a prism electrode having a Ti diffused waveguide and a proton exchange-type optical waveguide formed on a single crystal LiNbO3 wafer (see, e.g., Q. Chen et al., J. Lightwave Tech. vol. 12 (1994) 1401). However, these optical deflectors require an inter-electrode gap of about 0.5 mm which is a thickness of the LiNbO3 wafers. Accordingly their drive voltage is so high that even when a ±600 V drive voltage is applied, only an about 0.5° deflection angle can be obtained.
On the other hand, the optical deflector described in the Laid-Open Japanese Patent Application No. Hei 09-5797 comprises a thin film optical waveguide of a 600 nm-thick epitaxial PLZT film formed on (100) plane of an Nb doped conducting single crystal SrTiO3 substrate. In the optical deflector described in the Laid-Open Japanese Patent Application No. Hei 09-5797, the drive voltage is swept in a −12 V to +12 V range, whereby a deflection angle of 10.80° is obtained.
However, in the above-described optical deflectors having the optical waveguides formed of LiNbO3, PLZT, etc., refractive indexes of the optical waveguides change by an amount proportional to an applied voltage, and in order to retain a deflected state of light, a voltage must be kept applied. A deflected state at the time of application of a drive voltage cannot be memorized. When the supply of a source power is paused because of a power supply failure, the deflected states of respective optical deflectors must be set again.